Real-time Hardware-in-the-Loop (HIL) simulation is crucial for the comprehensive testing and validation of automotive Electronic Control Units (ECUs) before they are integrated into a vehicle. Robust HIL environments can easily interface with ECUs over Ethernet; however, critical components like Battery Management Systems (BMS) and sensors/actuators often rely on short-distance, low-latency protocols such as SPI. This thesis presents the design, implementation, and verification of a real-time communication bridge between Ethernet-based UDP protocols and full-duplex SPI interfaces, addressing the challenge of integrating such SPI-based devices into Ethernet-based HIL simulators. Implemented on STM32F207ZG Nucleo boards configured in a Master-Slave topology, the Master board interfaces with an external HIL environment (dSPACE or a Python-based prototype) via Ethernet (UDP protocol).